1. Field of the Invention
This invention relates to a disk, such as an optical disk, applied to a recording and/or reproducing apparatus of the magnet clamp type and more particularly to a disk having at the central portion thereof a disk hub attracted and supported by a magnet of the disk drive unit.
2. Description of the Prior Art
Up to the present, a disk such as an optical disk has been known and used as the recording medium for information signals.
In the recording and/or reproducing apparatus employing the disk as the recording medium, the recording and/or reproducing operation is performed by irradiating the rotary recording surface of the disk with a light beam emanating from a light source, such as a semiconductor laser, as the disk is rotated at an elevated speed of several hundreds to one thousand and several hundreds of revolutions per minute. For assuring the high speed rotation of the disk, there is provided a clamp means whereby the disk can be connected to the disk drive unit provided in the recording and/or reproducing apparatus for rotation at an elevated speed. As such clamp means, there is proposed a so-called magnet clamp type system according to which a metal plate is provided on the disk hub arranged at the central portion of the substrate of the disk so as to be attracted by a magnet provided on the disk driven unit. There is also proposed a disk applicable to a disk drive unit employing the magnet clamp type clamp means.
It will be noted that, in the case of a disk applied to the aforementioned disk drive unit of the magnet clamp system, a metal plate need be affixed to the disk hub provided to the center of the substrate of the disk. For this reason, the disk hub is constituted by a supporting member secured to the substrate of the disk and a magnetic metal plate for clamping. The supporting member is formed of synthetic material in order to be secured and consolidated to the substrate of the disk similarly formed of synthetic material. Thus the thermal contraction coefficient of the metal plate differs from that of the supporting member. Thus, when the metal plate is integrally attached to the supporting member by metal die molding, such as outsert molding, to constitute a disk hub, and the disk hub is secured as by ultrasonic welding to the substrate of the disk, an unnecessary stress may be induced at the welding surface of the substrate of the disk thus occasionally distorting its major surface. Such distortion in the major surface of the substrate of the disk may cause double refraction in the light beam incident on or reflected from the substrate of the disk at the time of recording and/or reproduction thus frequently causing errors in reading and writing information signals.
Thus there is proposed a disk provided with a disk hub wherein, for attaching the disk hub to the substrate of the disk without causing distortion at the major surface of the substrate of the disk, the supporting member and the metal plate constituting the disk hub are prepared separately from each other, the supporting member by itself is secured to the substrate of the disk and the metal plate is ultimately attached to the supporting member.
Such disk is shown for example in FIG. 1.
The disk 60 shown in FIG. 1 is engaged with and supported by one major surface 62a of a metal plate supporting member 62 by turning a metal plate 61 in a prescribed mounting direction, herein in the direction of an arrow marked X, with respect to the supporting member 62, such that engaging projections 63 on the outer periphery of the metal plate 61 will be engaged with mating engaging portions 64 of the supporting member 62. This supporting member 62 is attached to a substrate of the disk 65 by having its other major surface secured to the center of the major surface of the substrate of the disk 65.
In the above disk 60, when attaching the metallic plate 61 to the supporting member 62, retaining projections 68 of a jig arm 67 are engaged in a plurality of through-holes 66 formed on the perimeter of the metal plate 61 and the jig arm 67 is turned to cause the metallic plate 61 to be turned in a metallic plate containing section 69 of the metallic plate supporting member 62 for engaging the engaging projections 63 of the metallic plate 61 with the mating engaging portions 64 of the supporting member.
It will be noted that, once the metal plate 61 is attached to the metal plate supporting member 62, it should be secured against accidental detachment from the supporting member 62. To this end, a hook 70 is provided to each of the mating engaging portions 64 of the metal plate supporting member 62 to prevent accidental removal of the metal plate 61.
However, when these hooks 70 are provided to the supporting member 62, a considerable torque will be required in engaging the projections 63 in the mating engaging portions 64 over these hooks 70. Consequently, when engaging the metal plate 61 with the metal plate supporting member 62, an unnecessary stress is produced at the attachment surfaces of the supporting member 62 and the substrate of the disk 65. In addition, when the metallic plate 61 is turned in the direction of engaging the projections 63 of the metal plate 61, the force of rotation is also applied to the supporting member 62, so that the stress accompanying the force of rotation acts on the attachment surfaces of the supporting member 62 and the substrate of the disk 65, as the shearing force, thereby the force of securing the metal plate supporting member 62 to the substrate of the disk 65 being occasionally lowered.
It will be noted that, when the metal plate supporting member 62 is not secured sufficiently strongly to the substrate of the disk 65, a disk hub may be dismounted from the substrate of the disk under the force of attraction of a magnet secured to a disk table to effect magnetic clamping through magnetic attraction of the metal plate, at the time the disk is placed on or detached from the disk table of the recording and/or reproducing apparatus, with resulting malfunction of the disk.